Integral cooling system for rotary engine

ABSTRACT

A rotary combustion engine ( 12 ) with a self-cooling system comprises a heat exchanging interface for discharging excess heat from the rotary combustion engine ( 12 ), and a direct drive fan ( 44 ) integrated on the rotary engine output shaft ( 26 ) for providing a flow of forced air over the heat exchanging interface.

RELATED APPLICATIONS(S)

This application is a continuation of International Patent ApplicationNo. PCT/CA2004/000260 filed on Feb. 24, 2004, which claims benefit ofCanadian Patent Application Nos. 2,419,691 and 2,419,692 filed on Feb.24, 2003, all of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cooling systems for rotary combustionengines and, more particularly, to an improved and compact coolingsystem suitable for integration with an aircraft compound cycle engine.

2. Description of the Prior Art

There have been attempts to develop compound cycle engines havinginternal combustion engines or other cycle-topping and turbine engines,coupled together to provide a common output. See, for example. U.S. Pat.No. 4,815,282. In such systems, however, little focus is given toproviding a cooling system that is particularly adapted for integrationin a compact package suitable for aircraft applications. U.S. Pat. No.5,692,372 shows a fan system for cooling an internal combustion engine,however there is room for improvement. There is a need for an effectiveand compact cooling system.

SUMMARY OF THE INVENTION

It is therefore an aim of the present invention to provide a compact andefficient cooling system for a rotary combustion engine.

Therefore, in accordance with a general aspect of the present invention,there is provided a cooling system in combination with a rotarycombustion engine having an output shaft extending outwardly from anengine casing, the system comprising a heat exchanging interface fordischarging excess heat from the rotary combustion engine, and a directdrive fan integrated on the rotary engine output shaft for providing aflow of forced air over said heat exchanging interface.

In accordance with a still further general aspect of the presentinvention, there is provided a compound cycle engine comprising acompressor and a turbine section, at least one rotary combustion enginemechanically linked to said turbine section in order to provide a commonoutput, and a cooling system for removing excess heat from said rotarycombustion engine, said cooling system including a fan integrated to anddirectly driven by an output shaft of said at least one rotarycombustion engine.

In accordance with a still further general aspect of the presentinvention, there is provided a method of cooling a rotary combustionengine having an output shaft extending outwardly from an engine casing,the method comprising the steps of: providing a fan on said outputshaft, and directly driving said fan with said output shaft to induce aflow of forced air.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing the integration of the gas turbineengine and rotary machine using bevel drive and direct drive blower.;

FIG. 2 is a functional schematic diagram of the compound cycle engineillustrating the air flow path through the gas turbine and the rotarytopping device;

FIG. 3 is a conceptual isometric view of a turbo compound enginepackage;

FIG. 4 is a conceptual isometric view of the engine of FIG. 3, showingthe outer air cooling ducts in place;

FIGS. 5 a and 5 b shows the device of FIG. 4 in both turboshaft andturboprop installations; and

FIG. 6 is a schematic cross-sectional side view of a rotary toppingdevice with integrated toroidal cooler and cooling fan.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic representation of a compound cycle engine 10 of atype preferably provided for use in a variety of aero applications, suchas turboshaft, turboprop or APU (auxiliary power unit) applications.Referring to FIG. 1, it can be seen that the compound cycle engine 10generally comprises at least one rotary cycle turbine topping device(TTD) 12 (preferably 1 or 2, as indicated in FIG. 1) and a gas turbineengine 14, which acts as a turbocharger. Turbocharger 14 comprises acompressor 19, a first stage turbine 20 and a second stage or powerturbine 16. A hollow shaft 22 connects first stage turbine 20 tocompressor 19. The power turbine 16 is preferably a free turbine andincludes a power turbine shaft 28 concentrically disposed within thehollow shaft 22 for independent rotation with respect thereto. The shaft28 connects power turbine 16 to rotary machine 12 via a bevel gearset34. Preferably the bevel gear set 34 has a reduction gear ratio of 3:1.It is understood that the gear ratio could however be any desired gearratio. Compressor 19 communicates with an air intake 35 and a compressorscroll 24, the compressor scroll 24 leading to an inlet 37 of the rotarycycle topping device 12. The compressor scroll 24 preferably consists ofa split scroll (2*180 deg half scrolls), as indicated in FIG. 2. An airoutlet 39 of rotary machine 12 communicates with an exhaust duct 41 to aturbine volute 30 leading to the turbines 20 and 16. A wastegate 32selectively connects compressor scroll 24 and turbine volute 30 in fluidflow communication. The wastegate 32 preferably includes a selectivelyopenable blow-off valve. As best shown in FIG. 2, the waste gate orblow-off valve 32 selectively allows the compressor discharge to bypassthe rotary cycle topping device 12 and to “blow off” directly into theturbine volute 30 in order to prevent surge at low rotary cycle toppingdevice speed.

As shown in FIG. 1, the rotary cycle topping device 12 has an outputshaft 26. To facilitate neat and compact packaging suitable for aircraftuse, it is herein proposed to set the output shaft 26 of the rotarycycle topping device 12 at an angle θ of about 90 degrees, andpreferably less, to the power turbine shaft 28. The angle θ ispreferably 45 degrees or greater. The bevel gearset 34 is used tomechanically link the rotary topping device output shaft 26 and thepower turbine output shaft 28 together. The use of the bevel gearset 34advantageously provides for very short ducting from the compressor 19 tothe rotary cycle topping device 12 and the rotary cycle topping device12 to the compressor turbine 20 and the power turbine 16 while at thesame time providing a compact transmission. The compressor exit andturbine entry ducting 24 and 30 is hot, heavy and expensive and, thus,is preferably as short as possible. The length of the ducting shouldalso be minimal in order to minimize heat and pressure losses whichnegatively affect the overall engine efficiency.

By so orienting the rotary cycle topping device 12 with respect to thepower turbine shaft 28 and by using a bevel gearset, the envelope andfrontal area of the engine 10 can also be minimized. This can be readilyappreciated from FIG. 3 which shows a pair of rotary cycle toppingdevices 12 installed at the front of the engine 10 on opposed sides of agearbox 17, the rotary cycle topping devices 12 being oriented atapproximately 90 degrees to the main engine axis. The resulting packagevery much resembles commercially available turboprops and turboshaft gasturbine applications and can conceivably be installed in existingaircraft nacelles or engine bays.

Another advantage provided by the above compact packaging configurationis that cooling air can be drawn along the main cycle air from a singleinlet 35 (FIG. 3) at the front of the engine 10.

While the rotary cycle topping device(s) could be placed in parallelwith the compressor turbine rotor with a relatively short ducting to thecompressor and turbine, a potentially heavy idler gear train would beneeded. Also the resultant frontal area would be high and not sosuitable for aero engine installation.

Inline placement of the rotary topping device(s) tends to lead to longducts from either the turbine or compressor to the rotary toppingdevice(s) as well as potentially requiring long installation. Theabove-described used of a bevel gearset to mechanically linked the powerturbine shaft 28 to the output shaft 26 of the rotary cycle toppingdevice 12 is, thus, advantageous as compared to the other contemplatedalternatives.

More specifically, as shown in FIG. 1, the bevel gearset 34 generallycomprises a first bevel gear 36 rigidly mounted to the rotary cycletopping device output shaft 26 for meshing engagement with a secondbevel gear 38 provided at the front end of the power turbine shaft 28. Athird gear 40 is rigidly mounted at the distal end of the rotary cycletopping device output shaft 26 for meshing engagement with a fourthbevel gear 42 provided on a shaft 18, which is connected to a load, suchas a propeller (FIG. 5 b), a generator, a tachometer, a helicopter rotor(FIG. 5 a), a starter (FIG. 3), an oil pump (FIG. 3), a fuel pump (FIG.3), a cooling fan, and a load compressor. Accordingly, the shaft 18 isdirectly drivingly connected to the rotary cycle topping device outputshaft 26 and indirectly drivingly connected to the power turbine shaft28 through the rotary topping device output shaft 26. The outputs of therotary cycle topping device 12 and power turbine 16 are thus linkedmechanically to drive the shaft 18. They both cooperate to provide theshaft horsepower required to drive the load coupled to the shaft 18. Atengine start-up, the rotary cycle topping device 12 does most of thework, whereas under normal operating conditions, the power turbine 16contributes significantly to the total power output on the shaft 18.

It is understood that the gearset 34 does not need to be a doublegearset and that any gearset that permits coupling of two non-parallelshafts could be used as well. All shafts 18, 22, 26 and 28 have suitablebearings 51.

As shown in FIG. 1, rotary engine shaft 26 is also connected to a fan orblower 44 having a fan air inlet 46 and a fan air outlet 47communicating via ducting 49 to an oil cooler 50.

The rotary cycle topping device 12 may be of any suitable design, suchas those disclosed in U.S. Pat. No. 5,471,834, U.S. Pat. No. 5,522,356,U.S. Pat. No. 5,524,587 and U.S. Pat. No. 5,692,372, to name a few,though there are certainly others available as well, as will beunderstood by the skilled reader. The contents of all of these documentsare hereby incorporated into this disclosure by reference. It is notedthat the cycle topping device does not necessarily have to be aninternal combustion engine, the only requirement being that it producesthe input (i.e. hot stream of gas) needed for the turbines to operate.For instance, a wave rotor engine coupled to a combustor couldpotentially be used for topping or providing an energy input to the gasturbine cycle.

As shown in FIG. 2, the rotary cycle topping device 12 preferablygenerates rotary movement through a sliding vane rotor 29 to drive theoutput shaft 26. A fuel-air mixer 27 is provided in the ducting betweenthe compressor scroll 24 and the rotary cycle topping device inlet 39 toinject fuel in the compressed air before it flows into the rotary cycletopping device 12. A low speed enrichment throttling valve 31 isprovided in the ducting just upstream of the fuel-air mixer 27 to adjustthe quantity of air entering into the fuel and air mixture. It can bereadily appreciated from FIG. 2, that the gas generator (i.e. thecompressor 19 and the compressor turbine 20) does not drive anyaccessories, its main function being to turbocharge the rotary cycletopping device 12. It is the rotary cycle topping device 12 and thepower turbine 16 that provides the require shaft horsepower to drive theaccessories. via a gearbox 17 (FIG. 3). The shaft 26 act as a powertake-off shaft for driving the accessories. The term “accessories” isherein intended to generally refer to gas turbine components that needto be driven and which does not provides any propulsive forces. Forinstance, the accessories could take the form of a fuel pump, an oilpump, an air pump, a starter, a tachometer, a generator and a loadcompressor.

Referring now to FIGS. 5 a and 5 b, shown is the compound cycle engine10 in turboshaft and turboprop installations, respectively. In FIG. 5 a,the engine 10 is used to drive a helicopter rotor 53. In FIG. 5 b, theengine drives a propeller 55. In the turboshaft application, the airintake is located at the top of the engine 10, whereas in the turbopropapplication, the air intake 35 is located on the front side of theengine 10.

In use, incoming air flowing through the air intake 35 is compressed bythe compressor 19 and directed to the inlet 39 of the cycle toppingdevice 12 via compressor scroll 24. Fuel is introduced into thecompressed air flow immediately prior to its entry into the rotary cycletopping device 12 by known means as schematically depicted at 27 in FIG.2. The low speed enrichment throttling valve 31 (FIG.2) adjusts thequantity of air entering into the fuel and air mixture. The fuel/airmixture is then further compressed by the rotary motion of the rotor 29before being ignited. The resultant combustion gases are then expandedto drive the rotor 29 and, thus, the shaft 26, before being exhausted.The combustion gases are directed into the compressor turbine 20 and thepower turbine 16 via the turbine volute 30. The compressor turbine 20and the power turbine 16 extract energy from the expanding combustiongases, converting the energy into shaft horsepower to respectively drivethe compressor 19 and the shaft 18 as well as other accessories. In use,shaft 22 typically rotates at about 60000-70,000 rpm while shaft 28rotates at about 50,000 rpm. The bevel gearset 34 will provide areduction of about 3:1. While output bevel gearset 34 will provide anoutput shaft speed as required, such as 6,000 rpm for a turboshaft or2,000 rpm for a turboprop. The rotary machine will have a rotationalspeed of about 15,000 rpm. The above speeds are given for exemplarypurposes only and are thus not intended to be exclusive.

In operation, the blow-off valves 32 are typically opened where there isa mismatch between the flow capacitors of the rotary cycle toppingdevice 12 and the turbocharger 14 such as might occur at part speedoperating conditions.

The above-described combined cycle engine offers high thermal efficiencybecause of high cycle pressure ratio and temperature provided by theclosed volume combustion of the rotary cycle topping device 12. Thecombined cycle also provides for the reduction of the size and theweight of the turbomachinery as compared to a conventional single cyclegas turbine engine at the same horsepower shaft or thrust because of theincreased power per unit mass airflow.

Furthermore, the integration of a rotary combustion device (i.e. thepreferred embodiment of the cycle topping device 12) into a gas turbineengine is significantly advantageous in term of fuel efficiencyparticularly when operating at reduced power.

The rotary combustion cycle topping device(s) 12 generate(s) heat duringoperation which must be dissipated in order to prevent overheatingthereof. Cooling requirements of such rotary internal combustion enginescan be higher than gas turbine engines and therefore achieving verycompact arrangements for cooling are important to making a practicaldevice for aviation and automotive applications.

As shown in FIGS. 1 and 6, a compact self cooling system for the rotarycycle topping device 12 can be achieved by integrating the axial bloweror cooling fan 44 directly on the output shaft 26 of the rotary cycletopping device 12. This is made advantageous by the relatively highoutput rpm of the rotary cycle topping device 12 (about 16000 rpm) whichmakes a high flow compact fan practical. There is no need forintermediate gears, chains or pulleys for driving the fan 44, as the fan44 is directly mounted on the rotary topping device output shaft 26,thereby providing for a very compact cooling arrangement.

As shown in FIG. 4, the direct drive cooling fan 44 draws ambient airthrough air cooling ducts 46 via cooling air intakes 48. The cooling airintakes 48 are located at the front of the engine 10 at a higherelevation or outboard position than the engine air intake 35 andlaterally with respect thereto. The compressor intake 35 corresponds tothe lowest flow section. This advantageously provides for more directflows of cooling air, which are much more difficult to design for. Theducting 46 to the fan 44 can advantageously be very short from the airintakes 48 due to the 90 degrees rotary topping device placement. Thecooling air is exhausted laterally through an exhaust port 59 of eachside of the engine 10. An optional duct aft 61 can be connected to theexhaust port 59 to discharge the cooling air axially along the sides ofthe engine 10.

The air cooling ducts 46 channel the air through a heat exchanger or anoil cooler 50 (FIGS. 1, 2, 3 and 6) to pick up the excess heat absorbedby oil or other coolant as it is circulated by a pump 51 (FIG. 6)through cooling passages 52 defined in the rotary topping device casing,as shown in FIG. 2. As shown in FIG. 6, the pump 51 is mounted in aclosed loop circuit 55 with the device 12 and the oil cooler 50 toensure a continuous re-circulation flow of oil. As the oil travelsthrough the oil cooler 50, it gives off heat to the forced air passingthrough the oil cooler 50. Then, the so cooled oil is re-circulatedthrough the cooling passages 52 in the rotary topping device casing toextract excess heat therefrom. The oil cooling is about 5% of the fuelinput.

As shown in FIG. 6, the oil cooler 50 is preferably provided in oneembodiment in the form of a toroidal oil cooler surrounding the faninlet on a downstream side of the rotary topping device 12. The toroidaloil cooler 50 is integrated to the rotary topping device 12 and extendsrearwardly therefrom. The toroidal cooler 50 is concentrically mountedabout the output shaft 26 and located radially outwardly of the device12. The toroidal oil cooler 50 provides a toroidal cooling path for theoil circulated by the pump 51, which is conveniently driven from thereduction gearbox 17. The fan 44 draws air radially inwardly through thetoroidal oil cooler 50. The toroidal cooler 50 defines air exhaustpassages 53 defining a bend from radial to axial. The hot air leavingthe toroidal cooler 50 is rejected axially rearwardly of the fan 44. Asillustrated in FIG. 6, the fan 44 is used mainly for the purpose ofproviding forced air through the oil cooler 50 in order to improvecooling efficiency. However, suction air from the fan inlet or deliveryair may also be used to cool the core of the rotary topping device 12 bycausing air to flow through axially extending passages 54 definedthrough the rotary topping device 12.

Instead of the toroidal oil cooler 50, it is contemplated to add acasing to the rotary combustion topping device 12 with cooling fins topermit direct air cooling of the device, but this alternative isconsidered less practical.

The embodiments of the invention described above are intended to beexemplary. Those skilled in the art will therefore appreciate that theforgoing description is illustrative only, and that various alternativesand modifications can be devised without departing from the spirit ofthe present invention. For example, the compressor and turbineconfiguration shown is only one of many possibilities. The ductingarrangement between successive components need not be exactly as shown,nor does the relative arrangement of components. Though the descriptionrefers generally refers to one rotary machine, it will be understoodthat one or more could be used in parallel or series. Accordingly, thepresent is intended to embrace all such alternatives, modifications andvariances which fall within the scope of the appended claims.

1. A cooling system in combination with a rotary combustion enginehaving an output shaft extending outwardly from an engine casing, thesystem comprising a heat exchanging interface for discharging excessheat from an oil supply of the rotary combustion engine, and whereinsaid heat exchanging interface includes a toroidal air-oil coolermounted about said output shaft, wherein said toroidal cooler is locatedradially outwardly about the rotary combustion engine and projectsaxially from one side thereof.
 2. A combination as defined in claim 1further comprising a direct drive fan integrated on the rotary engineoutput shaft for providing a flow of forced air over said heatexchanging interface.
 3. A combination as defined in claim 2, whereinsaid direct drive fan is disposed to draw air radially inwardly throughsaid toroidal cooler.
 4. (canceled)
 5. A combination as defined in claim1, wherein said toroidal cooler is concentrically mounted to the rotarycombustion engine.
 6. A combination as defined in claim 1, wherein acoolant is circulated by a pump through cooling passages defined in theengine casing in order to pick up excess heat and then fed to thetoroidal cooler before being recirculated back into the rotarycombustion engine.
 7. A combination as defined in claim 2, wherein thedirect drive fan draws air axially over parts of the rotary combustiondevice.
 8. A compound cycle engine comprising a compressor and a turbinesection, at least one rotary combustion engine mechanically linked tosaid turbine section in order to provide a common output, and a coolingsystem for removing excess heat from said rotary combustion engine, saidcooling system including a fan integrated to and directly driven by anoutput shaft of said at least one rotary combustion engine, and atoroidal cooler extending about an axis of said output shaft of therotary combustion engine, wherein said toroidal cooler is locatedradially outwardly about the rotary combustion engine.
 9. (canceled) 10.(canceled)
 11. A compound cycle engine as defined in claim 8, whereinsaid fan draws air radially inwardly through said toroidal cooler. 12.(canceled)
 13. A compound cycle engine as defined in claim 8, whereinsaid toroidal cooler is concentrically mounted to the rotary combustionengine.
 14. A compound cycle engine as defined in claim 8, wherein acoolant is circulated by a pump through cooling passages defined in theengine casing in order to pick up excess heat and then fed to the heatexchanger before being recirculated back into the rotary combustionengine.
 15. A combination as defined in claim 8, wherein the fan drawsair axially over parts of the rotary combustion device.
 16. A method ofcooling a rotary combustion engine having an output shaft extendingoutwardly from an engine casing, the method comprising the steps of:providing a fan on said output shaft, and directly driving said fan withsaid output shaft to induce a flow of forced air, providing a toroidalcooler radially outwardly about the rotary combustion engine, and usingsaid fan for drawing air radially through said toroidal cooler. 17.(canceled)
 18. A method as defined in claim 16, further comprising thesteps of: circulating a coolant through said engine casing to pick upexcess heat, directing the coolant from the engine casing to thetoroidal cooler and then back into the engine casing.
 19. A combinationas defined in claim 1, wherein a pump is provided to circulate oilthrough the rotary combustion engine to extract excess heat therefrom.